In gas turbine engines, such as aircraft engines, air is drawn into the front of the engine, compressed by a shaft-mounted compressor, and mixed with fuel in a combustor. The mixture is then burned and the hot exhaust gases are passed through a turbine mounted on the same shaft. The flow of combustion gas expands through the turbine, which in turn spins the shaft and provides power to the compressor. The hot exhaust gases are further expanded through nozzles at the back of the engine, generating powerful thrust, which drives the aircraft forward.
Because engines operate in a variety of conditions, foreign objects may sometimes undesirably enter the engine. More specifically, foreign objects, such as large birds, hailstones, sand and rain may be entrained in the inlet of the engine. As a result, these foreign objects may impact a fan blade and cause a portion of the impacted blade to be torn loose from the rotor, which is commonly known as fan blade out. The loose fan blade may then impact the interior of the fan casing causing a portion of the casing to bulge or deflect. This deformation of the casing may result in increased stresses along the entire circumference of the fan casing.
In recent years composite materials have become increasingly popular for use in a variety of aerospace applications because of their durability and relative light weight. Current composite technology typically uses material having a tri-axial braid. As the name suggests, tri-axial braid generally consists of three fiber tows interwoven to form a braided ply of material. Although braided composite materials can provide superior weight and impact resistance properties when compared to non-composite materials, improvements can still be made.
For example, tri-axial braid material can often support only a defined maximum amount of applied tension beyond which the fiber architecture of the material will undesirably distort. Moreover, layered plies of tri-axial braid material can exhibit a degree of interlocking, which can make delamination difficult to ensure during impacts. This can result in a limited degree of impact energy dissipation. Additionally, the complexity of the braid design can make such materials costly.
Accordingly, there remains a need for articles, and in particular composite fan casings, made from more cost effective materials that can provide the desired delamination while supporting increased tension.